Complexity Tailored Design: A New Design Methodology for Databases With Incomplete Information

摘要

This paper introduces a new design methodology, complexity tailored degn, for databases containing incomplete information. The novelty of the approach is that it introduces query complexity as a consideration in database design. In general, the problem of evaluating queries in databases with incomplete information is intractable. Complexity tailored design consists in setting the values of database design parameters so as to guarantee the efficient (polynomial time) evaluability of selected queries. We develop this approach for OR-databases, which are obtained by extending relational databases with OR-objects that express restricted disjunctions; OR-objects occur naturally in planning. scheduling and design applications. We consider two design parameters: (i) typing that delimits the columns in which OR-objects may occur, and (ii) degree of co-reference that determines how OR-objects may be repeated within the database. We establish, for a broad class of queries in OR-databases, a complete syntactic characterization that classifies the data complexity of each query as being either in PTIME or co-NP complete, given a setting of the database design parameters. This characterization can then be used in complexity tailored design to determine "maximal" schemata for which the queries of interest to the user are evaluable in PTIME.